1. Field of the Invention
The present invention relates to an ultrasonic diagnosis apparatus capable of displaying a living body tomographic image generated on the basis of an ultrasonic echo signal which is received by transmitting an ultrasonic wave into a living body.
2. Description of the Related Art
A conventional ultrasonic diagnosis apparatus is commonly used which radiates an ultrasonic pulse to a portion in a living body to be diagnosed. The apparatus receives a reflected wave from the tissue of the living body and processes the reception signal of the ultrasonic echo signal to obtain a living body tomographic image. This apparatus can obtain a tomographic image without exposing a patient to X-rays when an X-ray photograph is taken, unlike an X-ray diagnosis apparatus. For this reason, the ultrasonic diagnosis apparatus is used for diagnosis in situations such as obstetrics-gynecology and the like.
In an ultrasonic diagnosis apparatus of this type, it has been known to obtain a tomographic image in a living body using a method called a synthetic aperture method. For example, this apparatus is disclosed in U.S. Pat. No. 5,349,960, International Patent Disclosure Number WO89/04143.
In the synthetic aperture method, ultrasonic transducers arranged in an array are changed over, and the transmission and reception of the ultrasonic wave are repeated by the selected ultrasonic transducer.
The ultrasonic waves are received by the respective ultrasonic transducers and converted into electric waveform signals. The electric waveform signals are digitized and stored in the form of time-sequential signals in a waveform memory, wherein each of the time-sequential signals represents the ultrasonic waveform in the sound-ray direction which is normal to the radiating surface of corresponding transducer.
Amplitude data is sampled and summed across the stored waveforms along a wavefront locus converting onto a desired focal point, to be synthesized into a reflection amplitude from the focal point. In this synthesis processing, the wavefront locus consists of time-of-flight data between the focal point and respective transducers.
In such an ultrasonic diagnosis apparatus using the synthetic aperture method, reception focusing can be freely performed throughout an imaging region. For this reason, an ultrasonic tomographic image having a high spatial resolution can be obtained.
The conventional ultrasonic diagnosis apparatus using a synthetic aperture method is designed to be adapted to various shapes and arrangements of array transducers such as linear shapes, concave shapes or convex shapes. Since each of these array transducers has its own direction and density of sound-ray distribution, the ultrasonic diagnosis apparatus performs a coordinate transforming process and an interpolation process at a digital scan converter (DSC). However, in order to perform such a coordinate transforming process and interpolation process in real time, a large and complex hardware arrangement is disadvantageously required. In addition, since interpolation is performed in accordance with a ratio of spatial distances from neighbor pixels in a conventional interpolation process, the image is still vague especially in a portion of coarse sound-ray distribution.
For an endoscopic application, the ultrasonic diagnosis apparatus is often required to be adapted to an ultrasonic probe for mechanical radial-scanning use. It is also necessary to perform a coordinate transforming process and an interpolation process. As a result, the cost increases, and the apparatus increases in size because a complex processing circuit is required.